From patchwork Thu Feb 2 05:25:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 51703 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp52709wrn; Wed, 1 Feb 2023 21:30:15 -0800 (PST) X-Google-Smtp-Source: AK7set83KmSJ6R9f8y66aiTjdyA4IBTsOgNvUVIyT/rNo7rH503MJr6WlmbXQdT3z0f4JNuXiec6 X-Received: by 2002:a05:6a21:33aa:b0:bc:fe7e:cfd9 with SMTP id yy42-20020a056a2133aa00b000bcfe7ecfd9mr6743292pzb.18.1675315815678; Wed, 01 Feb 2023 21:30:15 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1675315815; cv=none; d=google.com; s=arc-20160816; b=xaGuKi28fdnx+SjfoeN7XdJTz6HdhXvEe9EzpveD499CILhsBCIiBNDju5tkav4cLl jdn5HRxPbKLzLyiut/8k481oy6hazdatas/QfJqxJUhBEexH0mq41hg8XEsZoQRlXEf+ r6ZQj0o6aQeCkMtRqIPkHZ3tU/xyKF5z+pxUBjs6DdfHw3HmriTQGMQUDuI0NNMUPscZ EAJbrdg7v+QcyHYWtYr7dbvZAprHXu4Ti/OvidXx0BbIcIDEYSJus1IPp7MBZ8nhzndw iVnvCbZpofl0spihIfIO7+VdTdFfjKrjc/GSWKm9EBQCURHxESMxy3aKOSST0Jnziwfg Jrsw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=2pa3MaybsIFLyg6DJgnAqTcA2wieNTJIMwteW5Pm7LI=; b=kc+u8h2Mr0atFHKf1EVUGUTizdYimaNpm33KtB17RedOWKTf5cQ0sWqeHMTq6KCBUA stfOTRIfS8h9uiGeItl24UN1X0ESQ4gFgXc16RS3Ed+oGg6F7nivRl63xYGprTf9Bytl abuKEJHSCIwSCV1LRwVBuNUV78h0QfE0nmjYPpSZBHCi9zqJXHL7yp3u8dvAUyQWyWnL 2VSwR5wUc0qFb+EizfXjnb7fvfD2viDBt2kk8KGem9MC19ZIon/EuTfzkjCLrdSPa2l2 mYYkoRxsy/vppxordR5v49Ng//0i9UFgFIWLtWDHC2566ADqCEip9M8+2bdXvLnzV2DM zMPg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=UbZTii4m; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id v9-20020a63b649000000b004e1d512286esi1405624pgt.832.2023.02.01.21.30.03; Wed, 01 Feb 2023 21:30:15 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=UbZTii4m; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232024AbjBBF2v (ORCPT + 99 others); Thu, 2 Feb 2023 00:28:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229881AbjBBF2V (ORCPT ); Thu, 2 Feb 2023 00:28:21 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8FC618175; Wed, 1 Feb 2023 21:28:08 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 5F5BEB824B2; Thu, 2 Feb 2023 05:28:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB9C6C433EF; Thu, 2 Feb 2023 05:28:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1675315686; bh=lwTsMszefw5rHZqf0ZxqDJa/9KBH+8q5OL/uceUU0fo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UbZTii4mAY4ylde72kctTgOVOT9j9+lZ2Vteuc5VoE1N/86qwf/xs8LfXjEwvwQ7t yVccRvRKsAMqGd8b+G76VZmxQVmg4SWKJwUjwCf7XfPIqfvPGPtdcn7yf/pz0Ma3Ne d9NFQqhZwexls92DUssoVHJ4P8sBAD7QZ6XNbS3n20ivvvcWgZe6QKGLY71/jeXT/f TDUCnSUkcLYs1XasuexX5N99cJ0l5okNpbrau1/OhnRLwfLzBPuL6OhvigCCQGw//9 UNSkiDveRQe9DiAbKHKrrm3lau86pK3tDliQSowLQbfagSz3E3FPwgFChdEIz/pXaE SsvS9kNAHTwyQ== From: Eric Biggers To: stable@vger.kernel.org Cc: Harshit Mogalapalli , Kees Cook , SeongJae Park , Seth Jenkins , Jann Horn , "Eric W . Biederman" , linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, Luis Chamberlain Subject: [PATCH 4.19 09/16] exit: Put an upper limit on how often we can oops Date: Wed, 1 Feb 2023 21:25:57 -0800 Message-Id: <20230202052604.179184-10-ebiggers@kernel.org> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230202052604.179184-1-ebiggers@kernel.org> References: <20230202052604.179184-1-ebiggers@kernel.org> MIME-Version: 1.0 X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756695956555419561?= X-GMAIL-MSGID: =?utf-8?q?1756695956555419561?= From: Jann Horn commit d4ccd54d28d3c8598e2354acc13e28c060961dbb upstream. Many Linux systems are configured to not panic on oops; but allowing an attacker to oops the system **really** often can make even bugs that look completely unexploitable exploitable (like NULL dereferences and such) if each crash elevates a refcount by one or a lock is taken in read mode, and this causes a counter to eventually overflow. The most interesting counters for this are 32 bits wide (like open-coded refcounts that don't use refcount_t). (The ldsem reader count on 32-bit platforms is just 16 bits, but probably nobody cares about 32-bit platforms that much nowadays.) So let's panic the system if the kernel is constantly oopsing. The speed of oopsing 2^32 times probably depends on several factors, like how long the stack trace is and which unwinder you're using; an empirically important one is whether your console is showing a graphical environment or a text console that oopses will be printed to. In a quick single-threaded benchmark, it looks like oopsing in a vfork() child with a very short stack trace only takes ~510 microseconds per run when a graphical console is active; but switching to a text console that oopses are printed to slows it down around 87x, to ~45 milliseconds per run. (Adding more threads makes this faster, but the actual oops printing happens under &die_lock on x86, so you can maybe speed this up by a factor of around 2 and then any further improvement gets eaten up by lock contention.) It looks like it would take around 8-12 days to overflow a 32-bit counter with repeated oopsing on a multi-core X86 system running a graphical environment; both me (in an X86 VM) and Seth (with a distro kernel on normal hardware in a standard configuration) got numbers in that ballpark. 12 days aren't *that* short on a desktop system, and you'd likely need much longer on a typical server system (assuming that people don't run graphical desktop environments on their servers), and this is a *very* noisy and violent approach to exploiting the kernel; and it also seems to take orders of magnitude longer on some machines, probably because stuff like EFI pstore will slow it down a ton if that's active. Signed-off-by: Jann Horn Link: https://lore.kernel.org/r/20221107201317.324457-1-jannh@google.com Reviewed-by: Luis Chamberlain Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20221117234328.594699-2-keescook@chromium.org Signed-off-by: Eric Biggers --- Documentation/sysctl/kernel.txt | 9 +++++++ kernel/exit.c | 43 +++++++++++++++++++++++++++++++++ 2 files changed, 52 insertions(+) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index db1676525ca35..fd65f4e651d55 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -51,6 +51,7 @@ show up in /proc/sys/kernel: - msgmnb - msgmni - nmi_watchdog +- oops_limit - osrelease - ostype - overflowgid @@ -555,6 +556,14 @@ scanned for a given scan. ============================================================== +oops_limit: + +Number of kernel oopses after which the kernel should panic when +``panic_on_oops`` is not set. Setting this to 0 or 1 has the same effect +as setting ``panic_on_oops=1``. + +============================================================== + osrelease, ostype & version: # cat osrelease diff --git a/kernel/exit.c b/kernel/exit.c index 2147bbc2c7c32..fa3004ff33362 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -68,6 +68,33 @@ #include #include +/* + * The default value should be high enough to not crash a system that randomly + * crashes its kernel from time to time, but low enough to at least not permit + * overflowing 32-bit refcounts or the ldsem writer count. + */ +static unsigned int oops_limit = 10000; + +#ifdef CONFIG_SYSCTL +static struct ctl_table kern_exit_table[] = { + { + .procname = "oops_limit", + .data = &oops_limit, + .maxlen = sizeof(oops_limit), + .mode = 0644, + .proc_handler = proc_douintvec, + }, + { } +}; + +static __init int kernel_exit_sysctls_init(void) +{ + register_sysctl_init("kernel", kern_exit_table); + return 0; +} +late_initcall(kernel_exit_sysctls_init); +#endif + static void __unhash_process(struct task_struct *p, bool group_dead) { nr_threads--; @@ -924,10 +951,26 @@ EXPORT_SYMBOL_GPL(do_exit); void __noreturn make_task_dead(int signr) { + static atomic_t oops_count = ATOMIC_INIT(0); + /* * Take the task off the cpu after something catastrophic has * happened. */ + + /* + * Every time the system oopses, if the oops happens while a reference + * to an object was held, the reference leaks. + * If the oops doesn't also leak memory, repeated oopsing can cause + * reference counters to wrap around (if they're not using refcount_t). + * This means that repeated oopsing can make unexploitable-looking bugs + * exploitable through repeated oopsing. + * To make sure this can't happen, place an upper bound on how often the + * kernel may oops without panic(). + */ + if (atomic_inc_return(&oops_count) >= READ_ONCE(oops_limit)) + panic("Oopsed too often (kernel.oops_limit is %d)", oops_limit); + do_exit(signr); }